Some changes have been good. The grizzly bear population has recovered considerably since the early 1970s, when it was listed as threatened. Wolves were brought back in 1995. Wonderful. Given this greater diversity and abundance of big predators, other aspects of the ecosystem have begun to swing back toward a state of richness and diversity: elk, bison, antelope, deer. But many other changes have been for the worse. Whitebark pine trees, at high elevations, an important source of high-calorie food (their nuts) for grizzlies, have been dying off from a combination of factors related to climate change and invasive species. Invasive species—in the form of the lake trout in Yellowstone Lake—have also been linked to a crash of the native cutthroat trout, another important grizzly food. Meanwhile, visitor numbers have increased drastically, which represents another sort of problem for park management. And the big private ranches that lay within the periphery of the ecosystem, serving as winter range for elk, are susceptible to changes in ownership that might lead to subdivision, and therefore, a loss of crucial habitat. The Greater Yellowstone Ecosystem is a vast resource of wild lands, but its future is still up for grabs.